Enhancement: Speed limits overlay - show marker to indicate underground segments?

From https://github.com/CitiesSkylinesMods/TMPE/issues/1322#issuecomment-1023597131 :

Train Tracks works too but for underground it requires switching with PageDown to show signs. They probably forget about that, maybe add tiny sign or v so notify that something is there or another toggle to always show everything

[kvakvs]

Could potentially show down arrow icon and when hovered still allow speed set (maybe even show the current speed limit icon on hover)? Or have it so clicking the down arrow switches to undeground view?

We already have tools for switching underground view, its Pg Up, and Pg Down. Making more interactable markers is not useful for locations where more than 2 roads overlap (tunnel + bridge + some ground road), we tried to declutter screen and hide signs, instead of adding more signs. If you want to display some info in the underground markers, at least don’t make them interactable

[originalfoo]

Could potentially show down arrow icon and when hovered still allow speed set (maybe even show the current speed limit icon on hover)?

Or have it so clicking the down arrow switches to undeground view?